The discovery of a very cool, very nearby brown dwarf in the Galactic plane

P.W. Lucas, C. G. Tinney, B. Burningham, S. K. Leggett, D.J. Pinfield, Richard Smart, H.R.A. Jones, F. Marocco, Robert J. Barber, Sergei N. Yurchenko, Jonathan Tennyson, Miki Ishii, Motohide Tamura, Avril C. Day-Jones, Andrew Adamson, France Allard, Derek Homeier

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Abstract

We report the discovery of a very cool, isolated brown dwarf, UGPS 0722−05, with the United Kingdom Infrared Telescope Deep Sky Survey (UKIDSS) Galactic Plane Survey. The near-infrared spectrum displays deeper H2O and CH4 troughs than the coolest known T dwarfs and an unidentified absorption feature at 1.275 μm. We provisionally classify the object as a T10 dwarf but note that it may in future come to be regarded as the first example of a new spectral type. The distance is measured by trigonometric parallax as d= 4.1+0.6−0.5 pc, making it the closest known isolated brown dwarf. With the aid of Spitzer/Infrared Array Camera (IRAC) we measure H−[4.5]= 4.71. It is the coolest brown dwarf presently known – the only known T dwarf that is redder in H−[4.5] is the peculiar T7.5 dwarf SDSS J1416+13B, which is thought to be warmer and more luminous than UGPS 0722−05. Our measurement of the luminosity, aided by Gemini/T-ReCS N-band photometry, is L= 9.2 ± 3.1 × 10−7 L⊙. Using a comparison with well-studied T8.5 and T9 dwarfs we deduce Teff= 520 ± 40 K. This is supported by predictions of the Saumon & Marley models. With apparent magnitude J= 16.52, UGPS 0722−05 is the brightest of the ∼90 T dwarfs discovered by UKIDSS so far. It offers opportunities for future study via high-resolution near-infrared spectroscopy and spectroscopy in the thermal infrared.
Original languageEnglish
Pages (from-to)L56-L60
Number of pages5
JournalMonthly Notices of the Royal Astronomical Society: Letters
Volume408
Issue number1
DOIs
Publication statusPublished - 2010

Keywords

  • surveys
  • brown dwarfs
  • stars: low mass
  • INITIAL MASS FUNCTION
  • METHANE T-DWARFS
  • SKY SURVEY
  • SOLAR NEIGHBORHOOD
  • UKIDSS
  • COMPANION
  • PARALLAXES
  • AGE

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